1. Field of the Invention
The present invention relates to a semiconductor device and a method of manufacturing thereof, and more particularly to a semiconductor device which has a protective insulation film formed on a metal wiring miniaturized to a size less than a half micron and a method for manufacturing such a semiconductor device.
2. Description of the Related Art
A protective insulation film is formed on the top metal wiring layer of a semiconductor device for LSI and the like in order to prevent physical damage, contamination and moisture invasion. For a protective insulation film, a silicon nitride film grown at low temperature by plasma vapor deposition is commonly used. Also, a protective insulation film having a laminated structure with a silicon oxide film formed under a silicon nitride film to relieve the stress is used. For example, the protective insulation film with a laminated structure includes a silicon oxide film formed by vapor deposition technique using monosilane and oxygen or nitrogen oxide, or a PSG (phosphorus glass) film formed by doping a silicon oxide with phosphorus, or an SOG (spin on glass) film and a silicon nitride film having a thickness of about 1 .mu.m formed by plasma chemical vapor deposition using monosilane and ammonia or nitrogen gas.
These protective insulation films are selectively etched by dry etching or wet etching using a photoresist as a mask, and has an opening to define a bonding pad section for leading out an external electrode.
It should be noted that when a semiconductor device is miniaturized to less than a sub micron, the etching process on the metal wiring layers uses anisotropic dry etching, which results in the side wall of the metal wiring layers having a steep, almost vertical slope. As a result, voids are likely formed in certain areas on the metal wiring layers because a silicon oxide film and a silicon nitride film that compose a protective insulation film have poor adhesion and fluidity due to cusping. These voids become contamination traps. Also, the thickness of the silicon nitride film on side walls and corners of a groove of the metal wiring layers becomes extremely thin compared to that of the plane section of the silicon nitride film. As a result, moisture and contaminants would likely enter through the thin film portions, which presents long-term reliability problems.
Further, it is necessary to reduce inter-layer insulating film capacitance in order to increase the operation speed of the device. Therefore, conventionally, particular attention is paid to the inter-layer insulating film capacitance between a metal wiring layer and a substrate, or between upper and lower wiring layers. However, miniaturization of wiring space increases the effect of the inter-layer insulating film capacitance in the transverse direction. Therefore, when a protective insulation film has a structure in which a silicon nitride film having a high dielectric constant is present in a space between metal wiring layer formed in the same process, the inter-layer insulating film capacitance in the transverse direction cannot be ignored in light of electric characteristics such as the operation speed, etc.